Optical surface inspection of web with streak signal generating means

Abstract

An apparatus for detecting streaks in a moving sheet of material utilizes the signal generating and processing means of an existing spot/hole detection system which provides a series of spot measurement signals generated sequentially as a machine direction series of cross-machine sets and assigns a cross-direction location to each signal. Means are provided for calculating an exponential average of the signals for each of the cross-machine locations. This average is compared with a predetermined standard and an output signal, including a cross-machine location, is generated when the average exceeds the standard.

We claim: 
     
       1. In a material inspection apparatus for use in a sheet forming machine, said apparatus being of the type including: detecting means for providing a plurality of pixel signals, each having a magnitude representing the intensity of electromagnetic radiation received from a corresponding point on a moving sheet of material, said signals being generated sequentially as a series of cross-machine sets, said series extending in the machine direction; and   calculating means for calculating an exponential average of the signals for each of said cross-machine locations;   comparison means for comparing said exponential average for each of said cross-machine locations to a predetermined standard; and   output generating means for generating a streak signal when said exponential average exceeds said predetermined standard, said streak signal including a cross-machine location.   
     
     
       2. The apparatus of claim 1, wherein said calculating means calculates said exponential average in accord with the following formula:   NewAvg=(NewPixel-OldAvg)/N+OldAvg     where:   NewAvg is the new exponential average pixel value   OldAvg is the old exponential average pixel value   NewPixel is the signal value of the last pixel being included in the average   N is a filter constant   
     
     
       3. The apparatus of claim 1, wherein said calculating means calculates said exponential average in accord with the following formula:   NewAvg=[(NewPixel-OldAvg)+N*OldAvg]/N     where:   NewAvg is the new exponential average pixel value   OldAvg is the old exponential average pixel value   NewPixel is the signal value of the last pixel being included in the average   N=a filter constant   
     
     
       4. The apparatus of claim 1, wherein said calculating means includes a /N microchip. 
     
     
       5. The apparatus of claim 1, wherein said calculating means includes a (N-1) * microchip. 
     
     
       6. The apparatus of claim 2, wherein N is an integer. 
     
     
       7. The apparatus of claim 3, wherein N is an integer. 
     
     
       8. The apparatus of claim 2, wherein N=2 x  and x is an integer. 
     
     
       9. The apparatus of claim 3, wherein N=2 x  and x is an integer.